iOS 8 battery life: inconsistent?

So I've been running iOS 8 on my iPad Air and iPhone 5S for a while now. The battery life I've been getting on my iPad is very inconsistent. I've gotten well over 15 hours on one charge, then I struggled to get to 10 hours on the next charge... My usage is fairly consistent. So I don't know why the variance in battery life.

My iPhone on the other hand, with iOS 8, standby battery life is phenomenal. But usage battery life is about the same, or sometimes slightly worse.

What have been your experiences with battery life on iOS 8 from one full charge to the next full charge?

So I've been running iOS 8 on my iPad Air and iPhone 5S for a while now. The battery life I've been getting on my iPad is very inconsistent. I've gotten well over 15 hours on one charge, then I struggled to get to 10 hours on the next charge... My usage is fairly consistent. So I don't know why the variance in battery life.

My iPhone on the other hand, with iOS 8, standby battery life is phenomenal. But usage battery life is about the same, or sometimes slightly worse.

What have been your experiences with battery life on iOS 8 from one full charge to the next full charge?

My 5S has been doing the same thing as your iPad since iOS 7. I can't figure out why yet.